1. Field of the Invention
The present invention relates to an air-conditioning system, and more particularly to an apparatus and method for preventing an evaporator for the air-conditioning system from freezing.
2. Description of the Prior Art
An air-conditioning system is an apparatus for cooling an internal room by supplying an air which is cooled by an evaporating heat of a refrigerant.
Generally, the air-conditioning system has a compressor for compressing the refrigerant in a high temperature and pressure, a condenser for liquefying the gas-refrigerant, which is of high temperature and pressure by cooling, a receiver tank for separating a gas-refrigerant from a liquid-refrigerant which is supplied from the condenser so as to supply to an expansion valve, and an evaporator for evaporating an atomized liquid-refrigerant, which became low in pressure by passing through the expansion valve, thereby generating the cooled air.
In the air-conditioning system, when an electric power is applied to the air-conditioning system, the compressor is operated so that the refrigerant is compressed in the high temperature and pressure. The refrigerant, which is of high temperature and pressure, is supplied to the condenser, and is cooled by the air blown from a blower. The refrigerant, which is liquified in the condenser, is expanded by passing through the expansion valve, and the expanded atomized-refrigerant is sucked into the evaporator. The refrigerant, which is sucked into the evaporator, is evaporated while the surface of the evaporator is cooled by the air. Since the evaporator absorbs a surrounding heat thereof by the evaporating heat of the refrigerant, a cooling pin, which is formed at an outer surface of the evaporator, is cooled. At this time, the outer air passes through the blower, is cooled by the evaporator, and then is supplied to the room.
However, when the temperature of the evaporator surface is below 0 degrees or has a big temperature difference between the temperature of the outer air and the internal air, the surface of the evaporator frosts easily. Accordingly, the apparatus for preventing the surface of the evaporator from freezing, in which a throttle valve is mounted thereon for controlling an internal pressure of the evaporator to prevent the freezing of the evaporator surface, is disclosed. Which is issued to the U.S. Pat. No. 4,531,378.
FIG. 1 is a schematic view showing a structure of a conventional air-conditioning system, and FIG. 2 is a sectional view showing the throttle valve mounted on the conventional air-conditioning system. As illustrated, the air-conditioning system has a clutch 105 for transmitting or intercepting a power transmitted from an engine (not shown) to the air-conditioning system, a compressor 110 connected to the clutch 105 for compressing the refrigerant in high temperature and high pressure gas by a piston, and having a displacement varying device, a condenser 120 for condensing the gas-refrigerant supplied from the compressor 110, which is of high temperature and pressure, a receiver tank 140 for separting the gas from the liquid-refrigerant supplied from the condenser 120 and for supplying the liquid-refrigerant to the expansion valve 150, an evaporator 160 for evaporating the atomized-refrigerant supplied from the receiver tank 140 so as to absorb a surrounding heat, and a throttle valve 170 mounted between the evaporator 160 and the compressor 110 for controlling the pressure of the refrigerant so as to prevent the surface of the evaporator 160 from freezing.
When the internal pressure of the evaporator 160 rises or falls, the throttle valve 170 maintains the internal pressure of the evaporator 160 at a predetermined pressure so as to prevent the surface of the evaporator 160 from freezing.
The inlet 173 of the throttle valve 170 is connected to the evaporator 160, and the outlet 175 of the throttle valve 170 is connected to the compressor 110. The throttle valve 170 has a spring 172 mounted at an internal upper portion thereof, a diaphragm 174 connected to an end portion of the spring 172, and a valve body 176 connected to an end portion of the diaphragm 174.
If a cooling load of the evaporator 160 is lowered, the internal pressure of the evaporator 160 is lowered. Thus, the pressure of the refrigerant which flows into the throttle valve 170 is lowered. Accordingly, the elastic force of the spring 172 of the throttle valve 170 is greater than the pressure of the refrigerant which flows from the evaporator so that the valve body 176 moves in a lower direction. Accordingly, the valve body 176 intercepts a conduit 177 into which the refrigerant flows so as to prevent the refrigerant from flowing to the compressor 110. Consequently, the internal pressure of the evaporator 160 rises, the internal pressure of the evaporator 160 is maintained in a predetermined pressure. Accordingly, the throttle valve 170 prevents the temperature of the evaporator 160 from falling below 0 degrees, thereby preventing the evaporator of the air-conditioning system from freezing.
On the other hand, if the cooling load of the evaporator 160 rises, the internal pressure of the evaporator 160 also rises. Thus, the pressure of the refrigerant which flows into the throttle valve 170 rises. Accordingly, the elastic force of the spring 172 of the throttle valve 170 is smaller than the pressure of the refrigerant which flows from the evaporator 160 so that the valve body 176 moves in the upper direction. Accordingly, the conduit is opened, and the refrigerant is sucked into the compressor 110. Consequently, the internal pressure of the evaporator 160 is maintained at the predetermined pressure. Accordingly, the throttle valve 170 prevents the temperature of the evaporator 160 from falling below 0 degrees so as to prevent the evaporator 160 of the air-conditioning system from freezing.
On the other hand, a sensor for detecting the position of the valve body of the throttle valve 170 is provided. The sensor 180 detects the upper or lower movements of the valve body 176 and sends the signal to a control section 145. The control section 145 is connected to a displacement varying device 190 of the compressor 110. The control section 145 receives the signal from the sensor 180 for driving the displacement varying device of the compressor 110. Accordingly, the compressor 110 controls a compress capacity according to the cooling load of the evaporator 160 so as to prevent the evaporator 160 of the air-conditioning system from freezing.
However, since the conventional apparatus for preventing the evaporator of the air-conditioning system from freezing prevents the freezing of the evaporator by detecting the pressure of the refrigerant which flows into the compressor from the evaporator, it is difficult to adjust to the cooling load caused by the temperature difference between the temperature of the indoor air and the outdoor air.